The present invention relates to a simplified method of inspection for residual stress in transparent optical molded discs, particularly with polarized light inspection of transparent optical discs, and to an injection molding machine apparatus related to the method.
Apparatus for inspection of residual stress as used currently in the disc molding field has a polarizing plate on top of a box frame and another polarizing plate beneath the top polarizing plate which is kept at a given distance and parallel to the first plate, with polarized light meeting at a right angle (e.g., the polarizers are crossed). A fluorescent lamp is provided in the bottom of the box frame so that its light passes both polarizing plates. A molded disc is placed between the polarizing plates. If there is no residual stress in the molded disc, polarized light from the first polarizing plate will not pass the other polarizing plate, which causes molded disc to be dark overall in the range of vision. To the contrary, a molded disc with residual stress permits polarized light from a polarizing plate to pass partially to another polarizing plate because of the presence of anisotropy due to residual stress. The more stress or anisotropy, the brighter appears the inspected disc.
In another method, the residual stress of molded discs has been inspected by projecting the light of fluorescent lamp set in a factory""s ceiling onto a molded disc which is put between two polarizing plates placed in parallel with polarization meeting at a right angle.
The above-mentioned apparatus for inspecting molded discs requires a large space and is inconvenient for use in a narrow and littered molding location. Also, the above-mentioned method of inspecting a molded disc, when the two polarizing plates are supported by hand, is inappropriate for accurate inspection. The projected light is weak and, in addition, observation of the overall molded disc is not easy. The operator""s heat is prone to be conducted to the molded disc and the two polarizing plates due to hand""s gripping, which may be deleterious.
In light of the above-mentioned problems, it is an object of the present invention to provide a novel method, and injection molding machine, for inspection of residual stress of transparent molded discs using polarized light.
It is another object of the present invention to provide a novel method and an injection molding machine for inspecting the residual stress of transparent molded discs in which polarized light is produced from light emitted on a screen of a CRT or a liquid crystal panel provided in a display unit of an injection molding machine.
It is another object of the present invention to provide a novel method and an injection molding machine for inspecting residual stress of transparent molded discs in which polarized light is produced from emitted light on a screen of a CRT or liquid crystal panel which is kept bright white, with letters and/or figures erased.
It is another object of the present invention to provide a novel method and injection molding machine for inspecting of residual stress of transparent molded discs with polarized light using light emitted from a CRT screen or liquid crystal panel, which is kept white with a letter or figure erased, by adjusting a setting unit to set the molding conditions.